1. Field of the Invention
The present invention relates to apparatus designed to decode information contained on data cards, such as punched cards, for example. In particular, the present invention is directed to new and useful means and methods for synchronizing electronic data outputs representative of the information with the corresponding area of the data card where such information is located; and to new and useful means and methods of resynchronizing the electronic data outputs when an area of information on a data card is not detected at an anticipated time or location.
2. Description of the Prior Art
Card readers are employed to "read" coded information on data cards. Generally, the information is arranged on a card in rows and columns, and takes the form of a punched hole, a magnetic stripe, or the like.
It is essential that a card reader be capable of correlating specific data outputs with the corresponding column of information being read. If this correlation is not maintained, then a given output is incorrectly attributed to the wrong column; alternatively, when the information is not located at the appropriate area of the card, as a misregistered column, for example, an incorrect data output will result. These problems can arise from changes in the velocity of the data card through the reader caused by variations in drive motor voltage or temperature; or by misregistry of the punched holes or magnetic stripes.
Some of the above-described problems have been solved in prior art card readers by employing relatively expensive hysterisis-type synchronous motors. Other arrangements have utilized large timing discs having a plurality of striations per column, and have coordinated the data outputs with specific mechanical striations.
Phase comparison and referencing techniques are utilized in a number of applications in the electronic arts. Examples of patents disclosing such arrangements are U.S. Pat. Nos.: 3,238,459 to Landee; 3,150,352 to Einsel et al.; 3,010,028 to Mierhoff et al.; 3,201,759 to Kelley; 3,523,231 to Arthur et al.; 3,851,238 to Fletcher et al.; 3,420,989 to Sapp; 3,683,345 to Faulkes et al.; 3,336,534 to Gluth; 2,992,411 to Abbott; 3,181,122 to Brown; and 3,839,665 to Gabor.